Transportation Conformity: A Basic Guide for State and Local Officials

Introduction

The air quality provisions of the Clean Air Act (CAA) and the transportation planning provisions of Title 23 and Title 49 of the United States Code³ require a planning process that integrates air quality and transportation planning such that transportation investments support clean air goals. This process is known as transportation conformity and is carried out in accordance with 40 CFR Part 93⁴, U.S. Environmental Protection Agency's (EPA) conformity rule. Exhibit 1 below illustrates how conformity plays a central role as the link between transportation and air quality planning.

Exhibit 1 Conformity Links Air Quality and Transportation Planning

Transportation Conformity and Actions Subject to Conformity

Transportation conformity ("conformity") is a way to ensure that Federal transportation funding and approvals go only to transportation activities that are consistent with Federal clean air goals. Conformity applies to metropolitan transportation plans, metropolitan TIPs, and projects that are funded or approved by the Federal Highway Administration (FHWA) or Federal Transit Administration (FTA). Conformity requirements apply to areas that do not meet or previously have not met the air quality standards for ozone (O3), carbon monoxide (CO), particulate matter (PM-10 and PM-2.5) or nitrogen dioxide (NO2). These areas are known as nonattainment or maintenance areas, respectively. Exhibit 2 below shows all of the areas in the country that are nonattainment for the 8-hour ozone standard. Exhibit 3 shows all of the areas that are nonattainment for PM-2.5. For nonattainment and maintenance areas for these and other pollutants see 40 CFR Part 81 or www.epa.gov/oar/oaqps/greenbk/.

Exhibit 2 Attainment and Nonattainment Areas in the U.S. 8-hour Ozone Standard

Exhibit 3 Attainment and Nonattainment Areas in the U.S. PM2.5 Standards

Pollutants that Come from On-road Vehicles (e.g., cars, trucks, buses)

Transportation sources contribute to four of the six criteria pollutants for which EPA has established standards to protect public health and/or safety. The pollutants are: ozone (O3), carbon monoxide (CO), particulate matter (PM-10 and PM-2.5), and nitrogen dioxide (NO2). EPA recently began implementing new standards for PM-2.5 and O3. Appendix A provides basic facts about health impacts of these pollutants. Exhibit 4 shows the on-road percentage of total emissions by pollutant in 2002. Exhibit 5 shows the proportion of volatile organic compounds (VOCs), CO, NOx, PM-10, and PM-2.5 emissions from the various sources of pollution.

Description of a Conformity Determination

A conformity determination demonstrates that the total emissions projected for a plan or TIP are within the emissions limits ("budgets") established by the State Implementation Plan (SIP), and that transportation control measures (TCMs) in EPA-approved SIPs are implemented in a timely fashion. In certain cases, conformity may be demonstrated using other EPA-approved tests such as before a state has approved or found a motor vehicle emissions budget adequate for conformity purposes.

³ Title 23 and Title 49 of the United States Code (U.S.C.) codify various tansportation laws including the Transportation Equity Act for the 21st Century (TEA-21). These include transportation planning provisions that govern the programs of the Federal Highway Administration (FHWA) and the Federal Transit Administration (FTA).

⁴ The transportation conformity rule, as amended, is available at www.fhwa.dot.gov/environment/conform.htm.